Various types of motorized lifts are commonly used for transporting persons with disabilities up and down an incline or between different levels in a building. One common type of lift is the stair lift, which typically travels along a rail mounted adjacent a staircase. Such lifts may provide a relatively inexpensive and more practical alternative to passenger elevators in certain applications, such as where only a small incline has to be traversed (e.g., a single flight of stairs or a few steps), or in buildings which do not have room for a large passenger elevator.
Stair lifts typically take one of two forms, i.e., a wheelchair lift with a platform for carrying a wheelchair, or a chair lift in which the user sits on a chair that moves up and down the stairs. One example of a wheelchair stair lift is provided in U.S. Pat. No. 4,046,226 to Flinchbaugh, which discloses an elevator platform for wheelchairs that rides on parallel tracks mounted on either side of the staircase. Another wheelchair lift is disclosed in U.S. Pat. No. 3,966,022 to Cheney that travels along a rail or guide channel positioned on one side of the staircase.
An exemplary chair lift device for stairways is disclosed in U.S. Pat. No. 5,230,405 to Bartlet. This chair lift includes a rail incorporating a gear rack, a carriage unit having a motor and gear box which operatively engages the gear rack to provide motion of the chair lift, and a collapsible seat assembly mounted to the carriage unit. The carriage unit also incorporates a battery unit and control circuitry to control operation of the chair lift. The seat assembly is pivotable on a swivel mechanism which permits the seat assembly to be locked in different positions.
One difficulty that is sometimes encountered in the installation of stair lift systems is when the inclination of the stair railing changes, such as for stairways which have an intermediate landing. This can be problematic in that if the lift is attached to the railing at a fixed angle, the lift will tilt when it transitions between levels, potentially causing the user to fall off.
As a result, various stair lift systems have been developed for use in such applications that keep the lift level during travel. By way of example, European Patent Publication No. 560,433 to Van't Schip et al. discloses a gear-driven stairway chair lift which also includes a chair-leveling device. The leveling mechanism levels the chair based upon the position of the lift along the stairway. Another similar stairway chair lift is disclosed in U.S. Pat. No. 5,720,364 to Glover. The lift levels its chair based upon the angular position of the lift along a guide rail. The angular position is determined by counting rotations of the drive motor or drive gear.
U.S. Pat. No. 5,967,265 to Bruno et al. discloses a gear-driven chair lift which runs on a rail having a retaining surface and guide surfaces. The guide surfaces have a slope or degree of inclination which varies based upon the slope or degree of inclination of the rail, and the guide surfaces maintain the chair at a constant incline angle (i.e., level) despite the angle or curvature of the rail.
Japanese Patent No. 5,116,868 to Yoshiaki et al. discloses an elevator for a staircase that includes a driving body for guiding the elevator along a rail mounted along side the staircase. The drive mechanism is a gear that mates with a toothed track on the rail. The elevator body carries a chair, and a detecting sensor is used to detect an incline angle of the driving body relative to the rail. An angle adjusting means is used to adjust a relative incline angle between the driving body and the chair based upon the detected incline angle. Thus, the elevator maintains a constant incline position for the chair (i.e., horizontally level) while traveling up and down the staircase, even where the rail changes angles and is horizontal.
Despite the advancements in stairway lifts, these systems may not be suitable for use in transporting handicapped persons in other applications. By way of example, another situation in which handicapped users need to traverse an incline is in boarding ships. That is, even though many marine gangways have a flat ramp instead of stairs, it may still be difficult for a handicapped person to walk or move a wheelchair up or down a gangway at a fairly steep incline by themselves.
Yet, because marine gangways are often attached to ships or floating docks which go up and down with tidal changes, the incline of the gangway changes as well. Thus, stairway lifts that rely on the angle of the lift to the railing, or the angular position of the lift along the railing, would not be able to maintain a lift in a level position in traveling or loading/unloading positions.